John Moore/Getty Images(TUCSON) -- U.S. Border Patrol agents caught in a violent December standoff with illegal immigrants in Arizona fired the first shots, but with bean bags not bullets newly obtained records show.

At least one of the suspected bandits armed with AK-47 assault rifles returned fire, hitting Agent Brian Terry, who later died.

"When the suspected aliens did not drop their weapons, two Border Patrol agents deployed 'less than lethal' bean bags at the suspected aliens," FBI search warrant requests say according to the Arizona Daily Star newspaper, which first obtained the documents. The ammunition is designed to wound and take down targets not kill them.

"At this time, at least one of the suspected aliens fired at the Border Patrol agents. Two Border Patrol agents returned fire, one with his long gun and one with his pistol."

Officials have confirmed the agents hit one of the suspects -- Manuel Osorio-Arellanes -- who is the sole individual in custody but not charged with Terry's murder. He's awaiting a May trial for illegal re-entry to the United States after a previous deportation.